A study to enhance the value of natural silica sand from Tanah Laut, South Kalimantan, Indonesia has been initiated. A number of local sands were selected as the candidates for the study. The selected sand contained more than 90% quartz and was further processed to obtain a high purity initial powder using magnetic separation and immersion with HCl. The sealing materials were prepared by mixing the natural-sand-based silica (SiO2) powder with magnesia (MgO) and boria (B2O3) with composition of 70:10:20 by weight followed by uniaxial pressing and finally sintering at 1150°C for 1h and 4 h to produce ceramic composites. XRD measurement revealed that the ceramic contained quartz, protoenstatite, and clinoenstatite. The 1h and 4h ceramics exhibited 1.89% and 0.43% apparent porosity, 7.00 106 and 6.63106 cm electrical resistivity, 3.60 and 2.29 GPa Vickers microhardness, and 11.2010-6 and 11.5510-6 ppm/°C thermal expansion coefficient respectively. The 4h sample is more appropriate for sealing function in fuel cell than the 1h sample.

A prospective fuel cell sealing material using silica sand from Bancar, Tuban, East Java has been investigated. The investigation was aimed to enhance the value of such natural sand and was started by a treatment using magnetic separation and immersion with HCl to produce pure silica powder. Ceramic composites were then synthesized by a solid state reaction method by mixing the silica powder, magnesia (MgO), and 5-20wt% of boria (B2O3), pressing the mixture into pellets and finally sintering them at 1150 °C for 4 hours. By Archimedes method, it was found that the addition of B2O3 is favorable to reduce the porosity of composites with a maximum value reaching 0.68(0)% for the composite with 20% B2O3. An X-ray diffraction technique revealed that a liquid phase sintering had occurred, indicated by the appearance of quartz (SiO2), forsterite (Mg2SiO4) and protoenstatite (MgSiO3) in the sample without B2O3 and quartz and protoenstatite in the composites with 5 and 10 wt% of B2O3. Meanwhile, the composite SMB15h, in addition to quartz and protoenstatit, also contains a new phase, namely suanite (Mg2B2O5). In SMB204h, there are quartz and suanite.The phase compositions were determined using the Rietveld method from which thermal expansion coefficient values of 9.5-12 ppm °C-1 had been predicted. These results showed that natural-sand-based composites could fairly satisfy the required conditions of fuel-cell sealing materials.